Radio shielding for spark plugs



April 12, 1938. .1.4.1. MAs'cUcr-l 72,113,735

RADIO SHIELDING FOR SPARK PLUGS Original Filed June l2, 1935 lNvENToR dosffl/ J. Misa/cw ATTORNEY Patented Apr.` 12, 1938 UNITED STATES PATENT OFFICE RADIO SHIELDING FOR SPARK PLUGS Original application June 12, 1935, Serial No.

26,096. Divided and this application June 10,

1937, Serial, No. 147,452

4 Claims.

This invention relates to spark plugs and particularly to radio shielding for spark plugs. This application is a division of application Serial No.

26,096, filed June l2, 1935, now Patent No.

2,083,916, issued June 15, 1937.

Where radio receiving apparatus is used in proximity to. internal combustion engines it is necessary to shield the ignition of the engine including thespark plugs to prevent interference with radio reception. It is common practice to provide radio shielding by enclosing the spark plug in a grounded metallic casing and providing proper insulating means to space the shielding fromv the spark plugs.

Where a sparkV plug is thus shielded the heat generated during use of the plug cannot be readily' dissipated. Such heat may be transmitted to the. shielding cap and the insulated conductor supplying current to the spark plug with deleterious effects. The broad object of the present invention is to provide a radio shielding means for spark plugs so constructed that the excess` heat from the spark plug willl have no immediate effect on the dielectric portion of .the shield and on the yinsulation of the conductor supplying current to the plug.

Where the insulated conductor is inserted in a radio shielding means it has been observed that the heat to which the parts are subjected will cause the insulation of the'conductor to adhere tb the dielectric of the shielding cap and, in effect, become vulcanized thereto. This has not been desirable since it is necessary to remove the insulated conductorfrom the shielding cap from time to time for the purpose of inspection and service. Therefore, a specic object of this invention is to provide a radio shielding cap so constructed as to minimize the danger oi the insulated conductor adhering to the dielectric of the shielding means by reason of-the heat to which the parts are subjected. v

A further specific object of the invention is to provide aradio shielding means so constructed that an air space will bepermitted between the insulated conductor and 'the dielectric of the shielding means.

'I'he invention consists of the construction, combination and arrangement of parts as herein illustrated, described and claimed. y

In the accompanying drawing, forming part hereof, is illustrated one form of embodiment of the invention, in which drawing similar reference characters designate corresponding parts, and in which:

Figure 1 is a vertical section, partly in elevation,

showing the spark plug and the radio shielding cap together with the ignition conductor; and,

Figure 2 is a vertical section through the radio shielding cap.

'Referring to the drawing, the outer part of the spark plug comprises a shell Ii provided with external screw-threads I for engagement in an appropriate opening in a cylinder head. The lower part of the shell 6 is formed with an inwardly curved base 8 having formed therein a plurality of slots 9 to provide a plurality of sparking points or areas I0. 'I'he shell 6 is provided with an internal shelf or shoulder I I and the upper part of the shell 6 is provided with internal threads I2 to receive a retaining means as hereinafter described. A washer I3 may be disposed adjacent the threads I to insure a gas-tight seal between the shell 6 and the cylinder head of the engine which receives the spark plug.

Disposed in the shell 6 is a center electrode I4 having a tip I5 formed with a shoulder I6. Disposed around the electrode I4 is a mica tube I1. On the outside of the tube Il near the lower portion thereof is a stack of mica washers I8, and a. complementary stack of washers 24 are disposed around the upper portion of the tube I1. trally of the tube I1 is disposed a bushing I9 having a flange and a sealing hoop 22 having a flange 23. The upper end of the spark plug is provided with a metal head 25 formed with a recess 26 to receive a contact, as hereinafter described.

The upper end of the electrode I4 is provided with a bore 21 and the extremity 28 of the electrode I4 is turned over to seal the parts of the plug together. A washer 29 is disposed on thev flange 23 and the parts of the spark plug are held 3 in the shell 6 by means of a cap nut 30 having a threaded portion-32 to receive the radio shielding means, hereinafter described.I 'I'he structure of the spark plug per se Vforms no part of the present invention, but is claimed in the parent application Serial No. 26,096.

The radio shieldingv means comprises a metallic cap 33 which is adapted to be placed over the upper end of the spark plug. The cap 33 may -be in the form of an elbow as shown, or'may have a different shape. The lower edge of the cap 33 is formed with a bead'34 which is adapted to be engaged by a coupling nut 35 formed with a aiige 36 which is turned over the bead 34. The nut 35 is free to rotate on the cap 33 and is adapted to engage the threads 32 on the upper part of the retaining member while the lower skirt of the cap 33 contacts the member 30. In this way a good electric contact is made andthe cap 33 may Cen- D be readily removed for the purpose of inspecting or servicing the spark plug.

'Ihe cap 33 is provided with a dielectric lining 31 having a thickness sulcient to effectively in- .sulate the terminal 25 and the contact means 40 in which is threaded a Contact screw 4I to the lower end of which is connected a spring 42 adapted to make Contact with the terminal 25 of the spark plug. The upper end of the screw 4l is provided with a point 43 adapted to make contact with the conductor.

A conductor 44 surrounded by insulation 45 is provided to supply current to the spark plug. In the past, it has been the practice to extend the insulation 45 to the left hand end of the bore 3B and the point 43 of the screw 4l was used to pierce the insulation 45 to make contact with the `conductor 44. This practice causes burning of the insulation 45, which `is undesirable. In order to avoid this condition the conductor 44 is extended to the end of the bore 38 but the insulation thereof 45 is removed for an appreciable distance, as shown in Figure 1. A coil spring 45 is connected to the conductor 44 and surrounds the conductor. The contact screw 4I extends partially through the coil spring 4B to make an effective electrical contact by reason of the resiliency of the spring 46, and at the same time the danger of burning the insulation 45 is eliminated.

At the point where the conductor 44 with its insulation 45 leaves the cap 33, a conical packing 41 provided with a copper or other metallic re` Q lljorcing means 48 is disposed. 'I'he packing 41 'may be of the type shown in co-pending application, Serial No. 731,833, filed June 22, 1934, and not only provides a waterproof joint, but the metallic portion 48 serves to-improve the electricalvcontact between the cap 33 and a radio shielding conduit 49 which surrounds the conductor 44 with its insulation 45. The conduit 49 is provided on its end with a ferrule 50 formed with a ange l, and a coupling nut 52 serves to` hold the conduit 49 against the cap 33 by reason of engagement with threads 53 formed on the cap 33. The pressure of the ferrule 50 against the packing 41 has a tendency to force the packing 41 inwardly against the insulation 45, thereby holding the conductor 44 ilrmly in place and rcmoving any strain from the end of the conductor, which eliminates the possibility of breakage of the conductor 44 at the point of contact with the screw 4I.

The general structure of the shielding cap and contact means may be the same as shown in copending applications Serial No. 481,766, led September 13, 1930, and Serial No. 657,166, filed February 17, 1933. The structure of the conduit may be the same as shown in co-pending application Serial No. 657,167, iiled February 17, 1933.

Having thus fully described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In combination with a spark plug and an insulated cable therefor, a radio shielding cap to cover the upper end of the plug, said cap being formed with a bore to receive the insulated cable and the wall of said bore being provided with ribs to space the insulation of the cable from the wall throughout the portion of the bore adjacent the cable.

2. In combination with a spark plug and an insulated cable therefor, a radio shielding cap to cover the upper end of the plug, said cap being formed with a bore to receive the insulated cable and the wall of said bore being provided with ribs extending substantially the entire length of the bore to space the cable from the wall to prevent adherence of the insulation to the wall of the bore.

3. In combination with a spark plug and an insulated cable therefor, a radio shielding cap to cover the upper end of the plug, said cap being formed witha bore to receive the insulated cable and the wall of said bore being provided with a helical rib to space the cable from the wall.

l4. In combination with a spark plug and an insulated cable therefor, a radio shielding cap to cover the upper end of the plug, said cap being formed with a bore to receive the insulated cable and the wall of said bore being provided with a continuous helical rib to space the cable from the wall.

JOSEPH J. MASCUCH. 

